From 1981 to 1987, 305 patients underwent surgery in this department for thyroid disorders, including 7 reinterventions for total thyroidectomy, with a mortality of 0.75% and a specific morbidity of 13.4%. The overall incidence of post-operative parathyroid insufficiency was 4.6%. This was higher after bilateral thyroidectomy (7.6%) than after unilateral thyroidectomy (0.7%). The early parathyroid risk was also higher after surgery for hyperthyroidism (9.7%) than after surgery for euthyroid goitres (2.4%). The true incidence of post-operative parathyroid insufficiency can only be evaluated by systematic clinical and biological investigation. Parathyroid insufficiency is due to devascularisation of one or several parathyroids during the course of thyroidectomy, or occasionally due to accidental resection with the thyroid lobe. The prevention of post-operative parathyroid insufficiency requires a surgical technique which limits any devascularisation of the parathyroid glands and if the vascular supply to a parathyroid is put at risk then autotransplantation should be performed.